Adjusting doctor blade arrangement for use with a drum applicator

ABSTRACT

The present device includes a doctor blade mounted on a holder, which holder is further mounted on a pair of slideable rods. In addition, mounted on the holder are two threaded pivot members made of material which will not score nor scratch the drum, with which the doctor blade is used. The pivot members are adjustably disposed to come to rest against the drum. Further in addition, there is an eccentric cam disposed to abut one of said slideable rods and said last mentioned slideable rod is spring loaded to be held against said cam. Accordingly, as said cam is rotated it determines the &#39;&#39;&#39;&#39;at rest&#39;&#39;&#39;&#39; location of said engaged slideable rod and thus said holder. This last mentioned action causes the doctor blade to pivot or be partially rotated around the ends of said pivot members. In response to this action the doctor blade is located at a chosen distance from the drum (thereby determining the thickness of the material transported by the drum for application to a sheet of paper or the like). Because the holder is &#39;&#39;&#39;&#39;floating&#39;&#39;&#39;&#39; on the slideable rods, the holder will be moved toward and away from said drum, in response to any eccentricities or irregular surfaces of the drum, so that the layer of material that is being transported by the drum for application will have a constant thickness.

United States Patent Tobias 51 May 2,1972

[54] ADJUSTING DOCTOR BLADE ARRANGEMENT FOR USE WITH A DRUM APPLICATOR Philip E. Tobias, 1872 Watson Rd., Abington, Pa. 19001 221 Filed: Oct. 8, 1970 21 Appl.No.: 79,087

[72] Inventor:

Primary Examiner-John P1 McIntosh Artorne v-Wi1liam E. Cleaver 57 ABSTRACT The present device includes a doctor blade mounted on a holder, which holder is further mounted on a pair of slideable rods. in addition, mounted on the holder are two threaded pivot members made of material which will not score nor scratch the drum, with which the doctor blade is used. The pivot members are adjustably disposed to come to rest against the drum. Further in addition, there is an eccentric cam disposed to abut one of said slideable rods and said last mentioned slideable rod is spring loaded to be held against said cam. Accordingly, as said cam is rotated it determines the at rest location of said engaged slideable rod and thus said holder. This last mentioned action causes the doctor blade to pivot or be partially rotated around the ends of said pivot members. in response to this action the doctor blade is located at a chosen distance from the drum (thereby determining the thickness of the material transported by the drum for application to a sheet of paper or the like). Because the holder is floating" on the slideable rods, the holder will be moved toward and away from said drum, in response to any eccentricities or irregular surfaces of the drum, so that the layer of material that is being transported by the drum for application will have a constant thickness.

7 Claims, 2 Drawing Figures Patented May 2, 1972 INVENTOR. Philip E.T0bi0s QM W ATTORNEY.

ADJUSTING DOCTOR BLADE ARRANGEMENT FOR USE WITH A DRUM APPLICATOR BACKGROUND The use of doctor blades with devices that transport viscous material (which material should not exceed a certain thickness) is well known. Such devices as adhesive applicators, which are set forth in the U S. Pat. Nos. 1,355,219 and 3,338,211 employ doctor blades to remove the excess adhesive material from the transport means. The removal of excess adhesive insures a layer of adhesive of a certain thickness on the transport means and therefore ultimately on the item to which the adhesive is applied.

It has been recognized in the past that it would be highly desirable to provide an adjustable doctor blade in order to permit the user to change the thickness of the adhesive (or other materials being coated). The thickness of the adhesive film applied dictates the degree of tackiness of the coated material. In other words, the thicker the coating the more tacky it will be, hence the desirability to control the thickness.

In prior art arrangements, wherein the doctor blade has been adjustable, it has been accomplished by adjusting the blade to a new fixed position. In any such arrangements the drum must be precisely ground, perhaps by an order of magnitude greater than the thickness being controlled. For example, if the film or adhesive thickness which is desired is to be 0.001 inches with a precision of percent, then the drum T.I.R. (total indicator runout) should be 0.0002. It is apparent that such a close tolerance requires not only great machining accuracy but also requires very careful centering of the shaft and journals. It becomes further apparent upon consideration that such high tolerance fabrication is costly.

On the other hand it is the normal result of practical machining practice to produce a drum surface with high spots and such high" spots will intennittently reduce the gap between the doctor blade and the surface of the drum. Accordingly, the thickness of the adhesive will vary on the article to which it is applied. As will be understood from the discussion to follow the present invention overcomes the problem of inadvertently varying the thickness of the material applied to an article.

SUMMARY In accordance with the present invention there is a doctor blade rigidly mounted on a holder and hence the doctor blade cannot slip with respect to the holder in response to any vibrations or loosening screws. The holder is mounted on two shafts which are slideably and rotatably engaged with two slotted frames. The holder and one of the shafts is each independently spring-loaded so that the holder and blade are pushed at the assembly ,top toward the drum and at the shaft toward the face of an adjustment cam. In addition, (in the preferred embodiment) the holder has two nylon bolts located at its extremities and angled to come radially into contact with the drum. Since the bolts come in contact with the drum they act as pivots about which the holder is partially rotated. With the holder being partially rotated, as just described, the gap can be narrowed or widened. The holder is rotated as just described by means of the eccentric cam located on one of the slotted frames. This cam comes in contact with one of the two shafts mentioned above and can easily be rotated to slide or position the shaft and hence the holder. The positioning of the cam causes the partial rotation of the holder and hence the adjustment of the doctor blade gap.

In addition to the foregoing, the bolts act to follow the contour of the drum surface. The shaft on the side away from the adjustment cam is free to rotate or slide laterally in its slotted frame. This allows the pivots to follow the high points of the drum even if there is a snaking" or helical runout to the drum. Hence the doctor blade gap is automatically adjusted in response to the presence of high spots on the drum surfaces thereby permitting the layer of the adhesive to remain constant once it has been set despite any such high spots.

The features and objects of the present invention will be better understood from the description below taken in conjunction with the drawings in which:

FIG. 1 is a pictorial schematic of the invention in combination with the drum; and

FIG. 2 is a side view of the structure shown in FIG. 1 with a portion of the housing added.

In FIG. 1 there is shown a drum 11 which is mounted on a shaft 13. The shaft 13 is shown protruding from the drum 11 and has a counterpart on the right hand side of the drawing which is not shown. It should be understood that the shaft 13 is mounted on some further means so that the drum 11 can be rotated and in fact the shaft 13 is geared to some drive mechanism to actually rotate the drum 11. Since these additional devices do not represent the invention they are not shown and they are so well understood it is not necessary to show them.

Also shown in FIG. 1 is the doctor blade holder 15. The doctor blade holder 15 is mounted on a pair of shafts 17 and 18. The shaft 17 shown on the left hand side is a relatively long shaft in order to accommodate the spring 37. On the other hand the shaft on the right hand side of the drawing is relatively short compared to the shaft 17.

As can be seen in FIG. 1 there is a pair of threaded nylon bolts 19 and 21 which are mounted through the holder 15 to come in contact with the drum 11. The bolts 19 and 21 are disposed radially with respect to the drum 11, i.e., if their respective directions were continued they would form a radius of the drum 22. Although it cannot be seen in the drawing it should be understood that the Nylon bolt 21 also comes in contact with the drum 11 on the right hand side of the drum. While in the preferred embodiment the bolts 19 and 21 are made of nylon so that the bolts will not scratch nor score the drum, other suitable materials can be used. The bolts 19 and 21 are threaded and are passed through threaded apertures in the holder 15 in order that they can be adjusted by threading them into and out of the holder 15.

Mounted on top of the holder 15 is the doctor blade 23 which is secured to the holder 15 by the top plate 25. The top plate 25 is bolted to the holder 15 by virtue of the screws or bolts 27, 28 and 29. The top plate 25 when bolted to the holder 15 with the doctor blade lying therebetween serves to secure the doctor blade to the holder 15. It is now apparent that the doctor blade 23 is rigidly held by the holder 15. The angle of attack between the top of the blade and the drum may be at right angles or an acute angle with a tangential plane of the drum to effect a push or alternatively at an obtuse angle to effect a scrape or wipe of the excess material from the drum.

As can be further seen in FIG. 1 there are located on the top plate 25 three spring mechanisms 30, 31 and 32. As will be better seen in FIG. 2 these spring mechanisms 30, 31 and 32 actually are formed to be long enough so that they push up against the housing when the holder is in its proper location with respect to the housing. Since the springs 30, 31 and 32 are pushed by the housing, and vice versa, they force the doctor blade to move toward the drum 11. If the doctor blade 23 were free to move by virtue of its shafts 17 and 18, in the slots 33 and 35 then the holder mechanism with the doctor blade fastened thereto would simply slide backward and forward in response to the spring action of the springs 30, 31 and 32. However, as can be seen in FIG. 1, the shaft 17 comes into abutment with the eccentric cam 36. Hence, when the springs 30, 31 and 32 attempt to push the doctor blade and the holder 15 forward, the holder shaft 17 comes in abutment with the eccentric cam 36 and the holder tends to rotate on the shaft 17 toward the drum 11 until the bolts 19 and 21 contact the drum.

As can be further seen in FIG. 1, the shaft 17 is springloaded by virtue of the spring 37. The spring 37 is wound around the shaft 17 and the ends thereof come in contact with the housing in the same way as do the springs 30, 31 and 32. The spring 37 is so wound that it pushes the shaft 17 away from the housing and hence the shaft 17 is held in contact with the eccentric cam 36, but is free to rotate on its axis.

If the shaft 13 is not located in the center of the drum 11, then when the drum 11 rotates it will have high spots thereon in accordance with the off-center location of the shaft 13. When a high spot moves to the doctor blade location, this high spot will tend to cam the nylon bolts 19 and 21 outwardly and accordingly the holder 15 will be pushed away from the drum so that the distance between the doctor blade and the surface of the drum 11 will be held constant. As the high spot passes beyond the doctor blade the springs 30, 31 and 32 which are continually trying to push the doctor blade and the holder back toward the surface of the drum 11 will cause the bolts to follow the drum into the low spots and hence keep the doctor blade gap with respect to the drum surface constant. In addition since shafts 17 and 18 are free to independently move in their respective slotted frames the doctor blade will follow a helical configuration. In other words, if a high spot should occur at the right end of the drum but not at the left end of the drum, the fact the shaft 18 is free to slide in slot 35 will enable the right end of the doctor blade to follow the high spot while the left end remains in its normal position. The same performance could be expected on the left hand side of the doctor blade if the left hand side of the drum had a high spot and the right hand side did not.

If the doctor blade is to be adjusted it can be done so by moving the eccentric cam 36. As the high spot of the eccentric cam 36, or as the distance between the shaft and the axis of the cam, increases, the shaft 17 will be moved further away from the drum surface. Since the holder 15 is a rigid member, the holder follows the adjustment when the cam 36 is rotated. When such an adjustment is made, the springs 30, 31 and 32 which tend to push the doctor blade toward the drum simply rotate the doctor blade around the tips of the bolts 19 and 21. Hence, if the user wants to increase the gap between the doctor blade and the surface of the drum 11, the shaft 17 would be moved toward the drum by rotating the eccentric cam 36 so that there is a shorter distance between its periphery and its shaft. In this way the shaft 17 would move closer to the shaft of the cam 36 and the doctor blade 23 would be partially rotated around the pivots 19 and 21 away from the surface of the drum 11.

It becomes clear that if the doctor blade gap is to be shortened, the shaft 17 should be moved away from the surface of the drum 1 1 by urging it there from in response to rotating the eccentric cam 36.

In FIG. 2 there is shown a side view of the device shown in FIG. 1. The identification numbers are the same and hence there seems to be very little explanation necessary. In FIG. 2 there is shown a portion of the housing 38. It will be noted that the spring 30 is in contact with the housing 38 and hence because of that contact the spring 30 is pushing the holder assembly 15 and therefore the doctor blade 23 toward the surface of the drum 1]. It also can easily be seen in FIG. 2 that as the eccentric cam 36 is moved so that there is a greater distance between the shaft 17 and the shaft 39 of the eccentric cam, the holder 15 will be partially rotated in a counterclockwise fashion so that the doctor blade will be pivoted around the nylon bolt 19 to come closer to the surface of the drum 11. If the eccentric cam of course is moved so that the distance between the shaft 17 and the shaft 19 is shortened, then the doctor blade 23 will be partially rotated to increase the gap between it and the surface of the drum 11.

It can also be readily seen in FIG. 2 that the spring 37 is pushed by the housing 38 which action serves to push the shaft 17 into abutment with the cam 36.

Increasingly improved adjustment action is obtained by using a relatively large distance between the axis of shaft 17 and the drum contact point of bolt 19 as compared with the distance between the drum contact point of bolt 19 and the drum-edge of the projected doctor blade 23. Of course the larger this ratio of lengths, the greater must be the eccentricity of the cam to achieve a given drum-to-blade gap. The choice of parameters will depend upon the precision needed, range of gap sizes, eccentricity of the drum etc. For example, I have used a spacing of 1%. inches between the shaft 17 and the bolt 19 contact point, and a three-sixteenth inch spacing between the bolt 19 contact point and the projected doctor blade contact point, and a cam eccentricity of 0.028 to give a range of gaps from zero to approximately 0.005 inches with no observable variation in film thickness, even through the total indicator runout of the 4% inch diameter drum measures as much as 0.004 inches.

It should be understood that the doctor blade holder and assembly can be made of many forms of rigid material and in the preferred embodiment is made of aluminum with the doctor blade being madeof spring steel. It should also be understood that the springs 30, 31, 32 and 37 can be other forms of spring devices than the kind shown provided they are arranged to urge the shaft toward the drum. In FIG. 1 a cutaway reservoir 40 is shown with the viscuous material 41 held therein and it should be understood that the arrangement of the reservoir and material is not critical as regards to the present invention as long as the doctor blade is outside the material to effect a removal operation. It should be further understood that the eccentric cam 36 can be mounted on some structure other than the slotted front and the springs 30, 31, 32 and 37 can be cammed against some structure other than the housing 38.

What is claimed is:

1. An adjusting doctor blade device for use with a material transport means comprising in combination:

first and second shafts;

doctor blade holder means mounted on said first and second shafts;

first and second holding members, said first shaft movably mounted in said first holding member, said second shaft movably mounted in said second holding member;

first and second pivot elements, said first pivot element disposed to extend from said doctor blade holder in a first location to come in contact with a surface of said material transport means, said second pivot element disposed to extend from said doctor blade holder at a second location to come in contact with a surface of said material transport means, said first and second locations chosen to be at a discrete distance from one another whereby when said first pivot element is cammed by the surface of said material transport means said first shaft is caused to independently move in said first holding member and whereby when said second pivot element is cammed by the surface of said material transport means said second shaft is caused to independently move in said second holding member;

doctor blade means mounted on said doctor blade holder;

and

spring loading means disposed to urge said pivot elements against the surface of said material transport means whereby said doctor blade will be moved in accordance with the surface of said material transport means to maintain a constant gap therebetween.

2. An adjusting doctor blade device according to claim 1 wherein there is further included an eccentric cam mounted in close proximity to said first shaft so as to come in contact with said first shaft whereby said doctor blade holder can be partially rotated around said first and second pivot elements in response to said eccentric cam pushing against said first shaft.

3. An adjusting doctor blade device according to claim 2 wherein said first shaft is spring loaded to be forced against said eccentric cam.

4. An adjusting doctor blade device according to claim 1 wherein said material support means is a drum and wherein said first and second pivot elements are disposed to come in contact with said drum at a radially located position.

5. An adjusting doctor blade device according to claim 1 wherein said first and second pivot elements are fabricated from nylon.

6. An adjusting doctor blade device according to clam 1 wherein said first and second pivot elements are disposed at substantially the opposite ends of said doctor blade holder.

7. An adjusting doctor blade device according to claim 1 wherein said first and second pivot elements are formed to be 5 adjustable toward and away from said material transport means whereby the gap between said doctor blade and the surface of said material transport means can be altered.

* I! IR 

1. An aDjusting doctor blade device for use with a material transport means comprising in combination: first and second shafts; doctor blade holder means mounted on said first and second shafts; first and second holding members, said first shaft movably mounted in said first holding member, said second shaft movably mounted in said second holding member; first and second pivot elements, said first pivot element disposed to extend from said doctor blade holder in a first location to come in contact with a surface of said material transport means, said second pivot element disposed to extend from said doctor blade holder at a second location to come in contact with a surface of said material transport means, said first and second locations chosen to be at a discrete distance from one another whereby when said first pivot element is cammed by the surface of said material transport means said first shaft is caused to independently move in said first holding member and whereby when said second pivot element is cammed by the surface of said material transport means said second shaft is caused to independently move in said second holding member; doctor blade means mounted on said doctor blade holder; and spring loading means disposed to urge said pivot elements against the surface of said material transport means whereby said doctor blade will be moved in accordance with the surface of said material transport means to maintain a constant gap therebetween.
 2. An adjusting doctor blade device according to claim 1 wherein there is further included an eccentric cam mounted in close proximity to said first shaft so as to come in contact with said first shaft whereby said doctor blade holder can be partially rotated around said first and second pivot elements in response to said eccentric cam pushing against said first shaft.
 3. An adjusting doctor blade device according to claim 2 wherein said first shaft is spring loaded to be forced against said eccentric cam.
 4. An adjusting doctor blade device according to claim 1 wherein said material support means is a drum and wherein said first and second pivot elements are disposed to come in contact with said drum at a radially located position.
 5. An adjusting doctor blade device according to claim 1 wherein said first and second pivot elements are fabricated from nylon.
 6. An adjusting doctor blade device according to clam 1 wherein said first and second pivot elements are disposed at substantially the opposite ends of said doctor blade holder.
 7. An adjusting doctor blade device according to claim 1 wherein said first and second pivot elements are formed to be adjustable toward and away from said material transport means whereby the gap between said doctor blade and the surface of said material transport means can be altered. 